In this paper,we point out that several assertions（Propositions 3.15 and 5.2（v）） in a previous paper by Majumdar and Samanta are not true in general,by counterexamples.
基金Supported by the Science Fund for Young Scholars of Shaanxi Normal University (Grant No 200701007)the Natural Science Foundation of Shaanxi Province (Grant No 2010JM1005)
文摘In this paper,we point out that several assertions（Propositions 3.15 and 5.2（v）） in a previous paper by Majumdar and Samanta are not true in general,by counterexamples.
